1. Field of the Invention
The invention pertains to the preparation of an aliphatic, cycloaliphatic, and/or aliphatic-cycloaliphatic di-and/or polyurethane by reacting a primary aliphatic, cycloaliphatic, and/or aliphatic-cycloaliphatic di- and/or polyamine, with an O-alkyl carbamate in the presence of an alcohol.
2. Description of the Prior Art
On an industrial scale, N-substituted urethanes are normally produced by the reaction of alcohols with isocyanates or by the reaction of amines with chlorocarbonates. The isocyanates and chlorocarbonates used in these reactions are obtained by phosgenation of the corresponding amines or the corresponding alcohols. Houben-Weyl, Methods of Organic Chemistry, Vol. 8, pages 137, 120 and 101, (Georg Thieme Publishers, Stuttgart, 1952). These processes are very expensive and phosgene must be used with care because of its potential danger to man and the environment.
N-substituted urethanes are used as intermediates and end products. For instance, German Published Application No. 26 35 490 and U.S. Pat. No. 3,919,278 disclose the use of N-substituted urethanes for the manufacture of isocyanates. Because of their utility, many attempts have been made to develop better methods for preparing N-substituted urethanes. These methods and their shortcomings will be discussed.
German Published Application No. 21 60 111 describes a process for the manufacture of N-substituted urethanes by reacting an organic carbonate with a primary or secondary amine in the presence of a Lewis acid. There are several problems with this process. The conversion rates are rather low and the reaction times are long. Furthermore, N-alkylarylamines are always produced as by-products.
U.S. Pat. No. 2,834,799 describes a process for making carbamic and carbonic esters by the reaction of urea with alcohols in the presence of boron trifluoride. The problem with this method is that the boron trifluoride is required in equimolar quantities so that at least one molecule of boron trifluoride is used per molecule of produced carbamic ester and at least two molecules of boron trifluoride are consumed per molecule of carbonic ester. This process is not only expensive, but it causes problems in the environment because the boron trifluoride is produced in the form of the H.sub.3 N.BF.sub.3 adduct.
R. A. Franz et al, Journal of Organic Chemistry, Vol. 28, page 585 (1963) describe a process for making methyl-N-phenyl urethane from carbon monoxide, sulfur, aniline, and methanol. Very low yields are produced by this method; the yield does not exceed 25 percent even when there is a long reaction period.
U.S. Pat. No. 2,409,712 describes a process for making N-alkyl and N-aryl urethanes by the reaction of monoamines with urea (either N,N'-dialkyl- or N,N'-diarylurea is used) and alcohols at temperatures of 150.degree. C. to 350.degree. C. under increased pressure. It should be noted that this patent only describes the manufacture of N-alkylmonourethanes and does not mention the manufacture of N,N'-disubstituted diurethanes and polyurethanes. U.S. Pat. No. 2,677,698 also describes a process for the manufacture of N-substituted monourethanes. In this process, the urea is initially converted into the corresponding N,N'-disubstituted urea with monoamines, is then cleaned, and subsequently is reacted with an alcohol. The processes described are expensive and the yields are very low. Attempts to improve the yield by improving the methods of preparing and purifying the N,N'-disubstituted ureas have been unsuccessful.
Other processes have not been successful in eliminating the problems described thus far. U.S. Pat. No. 2,806,051 describes a process whereby N-substituted urethanes are produced by reacting n-hexylamine with urea and alcohol at a mole ratio of 1.0:1.2:2.0 at temperatures below 200.degree. C., preferably of 120.degree. C. to 160.degree. C. Even in the preferably used temperature range, this process produces only small yields of N-substituted urethanes if the reaction time is limited to a period which is practical in an industrial setting. In view of the problems with this process, it is not surprising that U.S. Pat. No. 3,076,007, which describes the manufacture of N-alkyl- and N-cycloalkyl urethanes, does not incorporate the abovereferenced methods in its process. It does, however, describe the reaction of phosgene with alcohols to form chloroalkylformates, and it describes their subsequent reaction with amines to form urethanes. It also discloses the reaction of amines with ethylene carbonate to form urethanes.
None of the references cited discloses the preparation of aliphatic and cycloaliphatic di- and/or polyurethane by reacting a diamine with an O-alkyl carbamate in the presence of alcohol at temperatures of 160.degree. C. to 300.degree. C. It is surprising that aliphatic and cycloaliphatic di- and/or polyurethane can be produced in one process stage with good yields by reacting an O-alkyl carbamate with a diamine in the presence of alcohol at temperatures of 160.degree. C. to 300.degree. C. It is known that ethyl carbamates in boiling dioxane do not react with amines [D.G. Crosby and C. Niemann, Journal of the American Chemical Society, Vol. 76, page 4458 (1954)], and that the reaction of N-alkyl urethanes with alcoholic ammonia solution at temperatures of 160.degree. C. to 180.degree. C. results in an alkaline solution from which amine hydrochloride, urea, alkyl urea, and alkyl urethane can be isolated after neutralization with hydrochloric acid [M. Brander, Rec. trav. chim., Vol. 37, pages 88-91 (1917)]. Moreover, the manufacture of N-monosubstituted carbamates from monoamines, urea and alochols, and/or the exchange of the amino group in the carbamates succeeds with small yields only.
Prior teachings also indicate that corresponding diureas are obtained from diamines and O-alkyl carbamates; for example, hexamethylenediurea is obtained from hexamethylenediamine and carbamates. It is also known that, although urea and alcohol may react to produce urethanes, they continue to react to form N,N'-di-substituted ureas in the presence of amines. See Houben-Weyl, Methods of Organic Chemistry, Vol. 8, pages 151 and 140, (Georg Thieme Publishers, Stuttgart, 1952). These side reactions decrease the yield of the desired product.
Furthermore, German Pat. No. 896 412 indicates that high molecular, spinnable condensation products may be produced from the diamides of carbonic acid such as urea and diamines. This result is likely to occur if the amino groups of the diamines are separated by a chain of more than three atoms. U.S. Pat. No. 2,181,663 and U.S. Pat. No. 2,568,885, for instance, disclose that high molecular polyureas with molecular weights of 8000 to 10,000 and greater, may be produced when diurethanes are condensed with diamines at temperatures of approximately 150.degree. C. to 300.degree. C. Moreover, mono- and polyurethanes can be split thermally into isocyanates, alcohols and possibly olefins, carbon dioxide, urea and carbodiimide, and these products can be split into products such as biurets, allophanates, isocyanurates, polycarbodiimides, and others. See The Journal of the American Chemical Society, Vol. 80, page 5495 (1958) and Vol. 48, page 1946 (1956).
In view of the problems identified in the prior art, it was surprising that our process, which involved very similar reaction conditions, would result in di- and/or polyurethane with very good yields. It was particularly surprising because when diurethanes were prepared from the products mentioned in the previous paragraph acccording to the reaction conditions of our invention, good yields did not result.